Sorry for the lack of clarification, is mail identities still enabled for the individual user (from the admin control panel)? So login to the admin interface, select a user and check out the features tab and look for Mail Identities, is it clicked or not clicked? If it is not clicked, you may want to file a bug in bugzilla. If it is clicked, un-click it and hit save, repeat for other users as necessary.

unticked

thanks for the reply,

its unticked, users cannot add new Identities but the can modify the existing
Identities maybe thats the way its supposed to work
but it would be nice to have the ability to disable modifying existing mail Identities